Communication system



F. R. LAMBERTY 2,419,958

COMMUNICATION SYSTEM Filed Aug. 23, 1944 3 Sheets-Sheet l May 6, 1947.

/VVE'NTOR ER. AMBERTV BV.

. W Q @WZL ATTORNEY WM Qm- L HHHMHWV N.;

May 6, 1947- F. R. LAMBERTY 2,419,958

COMMNICATION SYSTEM Filed Aug. 25, 1944v 3 Sheets-Sheet 2 v l Il wm w v Q l* oasEnv/Nc OPERATORS im Awa rae-maw:

/M/ENTOR E l?. LAMBERT? v A TIO/QNEV May 6, 1947.

F. R. LAMBERTY COMMUNICATION SYSTEM Filed Aug. 25, 1944 3 sheets-sheet :5'

Y /M/EA/TOR FT R. LAMBERT? A 7` TORNEV Patented May 6, 1947 CGMMUNICATION SYSTEM Frederick R. Lamberty, Brooklyn, N. Y., assigner to Bell rielephone Laboratories, Incorporated, New York, N. Y., a corporation of New York Application August 23, 1944, Serial N0. 550,699

11 Claims.

1 rhis invention relates to telephone systems and particularly to systems comprising dial impulse controlled automatic switches for completing connections between calling and called subscribers stations.

Objects of this invention are the improvement of service observing equipment in automatic telephone systems, the provision of more reliable means for service observing and prevention of false operations of the number recorder.

This invention is a service observing circuit arrangement for an automatic telephone system; which arrangement, according to one feature of the invention, comprises means including impulse counting relays for varying the capability of the impulse receiving means according to the character of the selector or register to which the impulses are being transmitted.

Another feature of the invention is the provision of means for preventing false operation of the impulse recorder in a service observing equipment when, during establishment of a desired connection on a call initiated over the subscribers line to which the service observing equipment is connected, the connection is extended from one switch to the next.

A better understanding of the invention will be facilitated by describing a telephone system in which the invention is embodied, one such system being shown in the drawing which forms a part of this spccication. The invention is, however, not limited in its application to the specic system shown but is generally applicable to automatic telephone systems.

Referring to the drawing:

Fig. 1 represents a telephone system comprising a private branch exchange and a, central oice; and

Figs. 2 and 3 represent service observing equipment, in the private branch exchange, embodying applicants invention.

The private branch exchange is represented in Fig. 1 by a subscribers station A, line LI and line circuit LCI, a line iinder LFI and connector CI having access to the line LI, a rst selector SI, another connector C2, a subscribers station B connected by a line L2 to terminals in the bank of connector C2, and a trunk circuit TCI individual to a trunk TI extending to the central omce. The central oice is represented by a line finder, a district selector, a register sender, a nal selector and a subscribers line L3 and station D.

The subscribers stations A, B and D are of the usual type provided in automatic telephone systems, a dial or other impulse sending device being provided at each station for controlling the switches through which connections are established. Theline finder, selector and connector switches in the private branch exchange are of the well-known two-motion step-by-step type. Reference may be had to pages 53 to 65, inclusive, of the second edition of Automatic Telephony, by Smith and Campbell, for a detailed description of the structure and operation of such switches when used as selectors and con- Reference may be had to the patent to R. L. Stokely No. 1,799,654, dated April 7, 1931, for a description of the operation of step-by-step line finders. The switches in the central oflice are of the panel type arranged for revertive control. Reference may be had to the patent to Stearn and Scudder No. 1,395,977, dated November 1, 1921, for a detailed description of the operation of a register sender and the operations of district and inal selectors of the panel type. Each of the line finder, selector and connector switches is represented by a set of brushes and either one or two sets of terminals, only so much of the associated apparatus being shown as is required for a full and complete description of applicants invention. The line nder LFI is represented by brushes 2|, 22 and 23 and a set of terminals Il to which the line LI is connected. The connector Ci is represented by a set of brushes and a terminal set I8, to which theline LI is connected. The selector SI is represented by brushes 3l, 32 and 33 and two sets of terminals 4D and 6D; the set of terminals 4G represents a level in the bank of selector SI giving access to connectors, the terminal set 40 being connected to the connector C2; and the set of terminals 60 represents a level in the bank of selector SI giving access to trunks to the central ofce, the terminal set being connected to trunk circuit TCI. The connector C2 is represented by brushes 4l, 43 and 49 and a set of terminals 5D to which the line L2 is connected.

rIhe service observing equipment shown in Figs. 2 and 3 is connected by means of a service observing cord SOC and jack OJ I with any subscribers line on which it is desired to observe. The jack OJ I is shown directly connected by conductors II I, II2 and H3 to the line circuit LCI of the subscriber station A; but this connection may be made in the manner described in the patent to J. W. Gooderham, No. 1,504,230, dated August 12, 1924. The service observing equipment includes key and telephone equipment for a monitoring operator and time and pulse recording equipment comprising a pen register mech- 3 anism for recording the dial impulses created by the operation of the dial at the station which is under observation on calls initiated at this station, and an electrically controlled time stamp for recording the time at which a call is initiated and the time the call is terminated. The pen register Amechanism comprises two electromagnets |02 and |03 the operation of each of which is effective to advance and mark the tape. The operation of electromagnet oi each call provides a space between calls and makes sure that the time stamp will not register twice in the same place. The time stamp is rep.- resented by the operating electromagnet |00. The time and pulse recording equipment further |02 at the beginning comprises a sleeve relay II8, a linerelay |20,-

auxiliary relays |2I, |22, I24,'I25 and |26,`thrm ionic valves |40, |43, |50 and |53, impulse relays |44 and |54, auxiliary relays |63, |65, |10 to I'IIl inclusive, impulse counting relays I8I to |85, inclusive,fand auxiliary relays |90 and 19|. A key |55 is `providedfor controlling the filament and anode-cathode vvoltages ofy valves |40, |43, |50 and |53.

Assume now that the subscriber at station A initiates a call by removing the receiver from the receiver hook thereby closing a circuit for operating the line relay I5. The operation of relay I connects the winding of relay I6, through conductor I4to the -test terminal of the line LI in'the banks of a-group of line iinder switches including the switch LFI. The operation oi relay |5raa1so connects ground to the start lead ST thereby eiecting the starting oi an idle line linder- Ain `the ygroup having access to the line L| in the -manner-set forth in the aforementioned patent to L.- .Sto,kely.v VAssuming the nder LFI to be the-zonemstarted in `Search of the calling line, ground; is temporarily connected through` conductor `24, to the Vtest brush 23V of line nder LEI and, when the'brushes 2|, 22 and 23 engage the terminal I1 connected to the line LI, a circuit isclosed'for operating -the cut-off relay I6. The closureof `this -circuit iseffective to stop the operation -of the line finder with the brushes 2|, 222 and 23 in engagement with the terminals I1 thereby completing a circuit for operating the line 'relay 35 ofthe first selector SI. The operation ofrelay 35 closes a circuit for operating the slowto-release relay 36 whereby ground is connected to sleeve conductor 275 to hold the line finder operated and to hold the cut-01T relay I6 after the ground temporarily connected to conductorg24 of the-linender is disconnected therefrom.` The linerelay I5 releases after the cut-on relay I6 operates thereby. disconnecting ground from the start lead ST. When the calling subscriber dials theirst digit of the number of the subscribers station with which connection is desired, the line relay` 35 is alternately released and reoperated thereby advancing the brushes 3|, -32V and 33 V`to the corresponding level of the terminal bank. KSelection of-an idle set of terminals in the selected level and operation of the cut-through relay 34are completed in usual and lwell-known manner, the connection from the calling line bethereby extended through brushes 2| and 22, throughront contacts of relay 34 and brushes 3| and 32, to the trunk, intermediate selector or connector connected to the terminals engaged by the brushes.

YIi the call is a local call and there are no intermediate selectors, the calling line is extended throughbrushes 3|, 32 and 33 to conductors' 4I,l

42 and'4'3V of the connector'CZ;

of the connector is thereupon operated in series with the conductors of the calling line, thereby closing a circuit for operating the slow-to-release relay 4B. Relay 46 connects ground through sleeve conductor 43, brush 33 of selector SI and a front contact of relay 34 of selector SI to the sleeve conductor 25 to hold thel relay 34 operated and to 'hold the line finder and"cut"ofi relay I6 all in usual manner. The aforementioned operation of relay 34 disconnects the line relay 35 thereby causing the successive release of relays 35 'and 36; When the calling subscriber dials the last two digits of the called subscribers nurnber, the connector'is operated under the control lof the line relay 45 to select the terminals 50 -of line relay 45 and conductors 4I and 42 thereby to effect any desired supervisory or charging operation as is well known in the art. When the connection is released at the called station, relay 44 releases to restore the normal connection between. the windings of line relay 45 and conductors 4| and '42. When the calling subscriber releases, relays 45 and 46 release in succession andthe connector C2 is restored to normal in usual manner. The release of relay 48 disconnects ground from conductor `43 thereby causing the release of selector S|, the release of line finder LFI and the release of the cut-off relay IE.

If the call is one completed through the central oilice the digit dialed vby the calling subscriber 'eiiects the operation of the 4selector SI to select a level in which the terminals are con.. nected'to'trunks to the central office, one such trunk TI being shown connected through trunk circuitTCI to the'set ofvterminals B0. The trunk circuit TCI may be similar tothe trunk circuit T--2disclosed in the 4patent to H. Hovland No. 2,247,055, dated June ,24, 1941. Upon selection Vofthe trunk 'circuit'TCL ground is connected to 'line Vfinder LFI and "a calling condi-tion is established over trunk TI whereby a line iinder in the centralfoice Vis operated to connect with the trunk T| thereby to effect the extension of the connection from the calling subscribers line in the private 0branch exchange to a district selector and to an idle register sender inthe central office. The nimpulse relay 8.9 in the register sender ls operatively responsive to the impulses created by the dialing of the succeeding digits of the called subscribers numberfandthesedigits are thereby registered in the -re'gister sender.v The district selector and succeedingselectors includingl a final selector are operated under control of the sender toex'tend the connection to a called subscribers line L3 and station D.

Assume now thatkey -|55is operated to prepare Ythe time and impulse recorder for operation and that there is no call in progress over the `connected subscribers line. The operation of |55 connects ground lto conductorV |59 to energizethefilaments of valves |40, |43, |50 and fore no voltage drop through resistorV |42. With no voltage drop through resistor |42, thecontrol grid of valve |43 is positive with respect to the cathode due to the voltage drop through resistor |51; and therefore the winding of relay |44 is operatively energized by the current in the anode-cathode circuit of valve |43. With relay |44 operated, conductor |36 is disconnected from negative battery through resistor |45. Since both the control grid of valve |50 and the cathode are at ground potential, there is current in the anode-cathode circuit of valve |50; and the voltage drop through resistor |52 in the anode-cathode circuit of valve |50 is suflicient to make the control grid of valve |53 negative with respect to the cathode, so that there is no current in the anodecathode circuit of valve 53.

The winding of relay |20 is normally connected between battery at the upper back contact of relay I|3 and the ring conductor or" the plug of service observing cord SOC; so that, when this plug is inserted in jack OJ I the winding of line relay |20 is connected to the ring conductor l2 of line LI in parallel with the lower winding of the line relay |5 of line circuit LCI. When the subscriber at station A removes the receiver to initiate a call, relays |5 and |20 are both operatively energized. Relay I 20 closes a circuit for operating relay |2|, The operation of relay |2| connects the ring conductor ||5 of cord SOC to battery through resistor |30 in parallel with the winding of relay |29; and the control grid of valve |40 continues to be negative with respect to the cathode. The operation of relay |2| connects the control grid of valve |50 to the tip conductor I of line LI, this connection being traced through resistor |34, inner left front contact of relay |2|, tip conductor ||5 of cord SOC, tip conductor of jack OJ I and conductor The control grid of valve |50 is thus rendered negative with respect to the cathode, the dierence in potential being equal to the voltage drop in the upper winding of relay I5. The current in the anode-cathode circuit of valve I 50 is thereby ended and the control grid of valve |53 becomes positive with respect to the cathode; whereupon relay |54 is operatively energized by current; in the anode-cathode circuit of valve |53. Relay |54 closes a circuit for operating relay |63, relay |63 being a slow-to-release relay which remains operated during the response of relay I 54 to dial impulses as hereinafter described.

When the line finder LFI connects to the line LI, the connection of ground to conductor I4 effects the operation of cut-oil relay I6 and the operation of sleeve relay ||4 of the service observing cord. Relay I6 causes the release of line relay I5 and also causes the release of relay |20 in case the operation of relay I5 occurs before the line is connected through the line nder to the line relay 35 of the selector SI. The operation of relay I5 also extends the ground from conductor i4, through conductor IIS, to maintain the operation of sleeve relay ||4 after the line relay I5 releases. Relay I|4 closes a circuit for operating relay II8; and relay IIB connects battery to conductor ||1 to light the lamp L at the service observing operators position to indicatethat a call is in progress over the Vline which is connected to the service observing cord SOC. If relay |20 releases prior to the operation of relay IIB, relay |2| is held operated and relay |22 is operated. by current in a circuit traced from battery through the windings of relay |2| andV |22 in series, a back contact of relay |25 and vconnects battery to conductor |56 and closes another circuit for operatively energizing the windings of relays |2I and |22, this circuit being traced from ground at the outer right iront contact of relay I 2|, through conductor I I9, and a front contact of relay I |8. The operation of relay |22 closes a circuit through the outer left front contact of relay |2|, front contact of relay |22, outer lower back contact of relay |25, outer right back Contact of relay |25, and the winding of relay |24. Relay |24 operates, closing a circuit for operating the time stamp electromagnet |00 and closing a circuit for operating the pen register electromagnet I 02. The operation of relay |24 also closes a circuit for operating relay |25, this circuit being traced from battery through the winding of relay |25, right front contact of relay |24, inner lower back contact of relay |26, front contact of relay |22 and outer left front; contact of relay |2|. Relay |25 locks to the same ground independent of relay I 24 and causes the release oi relay |24. The release of relay |24 opens the circuits for operating the time stamp electromagnet |00 and the pen register electromagnet |02.

When the line conductors and I2 are connected through brushes 2| and 22 of line finder LFZ, to the windings of line relay 35 of selector SI, the control grid of valve |50 continues to be negative with respect to its cathode due to the voltage drop through the upper winding of relay 35; and the control grid of valve |40 continues to be negative with respect to its cathode due to the voltage drop in the f upper winding of relay 35 and the voltage drop in the station loop. When the calling subscriber dials the first digit Y of the called number, the line relay 35 is alternately released and reoperated to selectively control the operation of the selector. The control grid of tube |40 remains negative during dialing; b-ut each time the dial opens the operating circuit of relay 35, the potential of the control grid of tube |50 is changed to ground potential since there is no longer any voltage drop in the upper winding of relay 35. Each time the control grid is at ground potential, the current in the anodecathode circuit of tube |50 causes a voltage drop through resistor |52 which makes the control grid of tube |53 suiciently negative with respect to its cathode to stop the current in the anode-cathode circuit and thereby cause the release of relay |54. Each time the dial recloses the circuit for operating relay 35, the control grid of tube |50 is rendered negative with respect to its cathode, the potential of the control grid of tube |53 is again rendered positive with respect to its cathode, and relay |54 reoperates. The release of relay |54 closes a circuit for operating relay |55, this circuit being traced from battery through the inner upper front contact of relay 8, conductor |65, winding of relay |65, lower back con tact of relay |10, lower front contact of relay |63, and conductor IGI to ground at the back contact of relay |54. Relay |65 locks under control of relay |10, closes a circuit for operating relay |13, closes a circuit for operating the pen register electromagnet |02, closes a circuit for maintaining the operation of relay |53, and closes a circuit for operating relay |10. Relay |13 closes a circuit for operating relay |14; and the operation of relay |14 releases pen register elece Vthe operation of relay |1| in Va. circuit which Vincludes the back contact of relay |12.

Relay |1I locks under control of relay |12, closes a circuit ,for operating relay |12, closes a circuit for holding relay |13 operated', closes a circuit through conductor |04 for operatingthe pen register electromagnet |03, and closes a circuit from ground through a front contact of relay |63, back contacts of relays |90 and |6|, conductor |80, middle upper front contact of relay |1|, and upper back contact of relay |11 for operating relay |15. The release of relay |65 opens the operating circuit of relay |13 and opens the holding circuit of relay |63. Relay 12'locks under the separate control of each of relays |1| and |10; and the operation of relay |12 causes the release of relay |1|. rThe release of relay |1| opens the holding circuit for relay |13, releases the pen register electromagnet |03, and renders effective a circuit for holding relay |15'operated and for operating relay |11. The last-mentioned circuit is traced from battery through the winding of relay |15, lower winding of relay |11, back contact of relay |16, upper front Contact of relay |15, conductor |80, back contacts of relays |90 and |9|, to ground at the upper front contact of relay |63. The operation of rela`y4|11 connects grounded conductor |86 to conductor |10 to eiect operation of the counting relay |8|. through its upper Winding, back contacts of relays |82, |83, |84 and |85, conductor |80, back'contacts of relays |90 and ISI, to ground at the upper iront contact of relay |63. When relay v|54 reoperates at the end of the rst dial impulse,

relay releases; and the release of relay |10 causes the release of relay |12. The release of relay |53, responsive to a second dial impulse in the train corresponding to the rst digit dialed, causes relays |65, |10, |1| and |12 to function in similar manner to that above described. The operation of relay |1| responsive to a second dial impulse closes a circuit from vbattery through the upper winding of relay |16, upper winding and front contact of relay |11, middle upper front Contact or" relay |1|, conductor |00, back contacts of relays |90 and |9| to ground at the upper front contact of relay |63. Relay |16 opens"the circuit through the winding of relay |15 and lower winding of relay |11, and locks through its lower winding until relay |'releases. When relay |1| again releases responsive to the reoperation of relay |56 at'the end of the second dial impulse, relays |16 and |11 release" thereby connecting conductor |63 to conductor |18 to'operate counting relay |82. Thus relays |15, |16 and |11 are operated under the control of relay |1| to connect ground to conductor |19 responsiveto each oddv numbered dial impulse in a train and toconnect ground' to conductor |18 responsive to each :even numbered dial impulse 'in a train. The counting relays are thereby operated in succession to indicate the digit dialed. The operationof each of relays |82, |83, |84 and |85 eiiects the'release'of the preceding counting relay and prepares an operating circuit for the succeeding counting relay. Relay i'operates'responsive to a sixth impulsebut does not cause the release of relay |35. Relay |86 locksover'conductor |23under the control of relays|22andr|2| and prepares .for therecperationV of-rela'y |8|;' A'seventh'im- Relay |8| locksV 8 pulse reoperatesrelay |81 and causes they release yof r.e1ay.l5 Relayw?. :|83 andl |84, arefsucces'sively reoperated` by eighth, ninth and tenth impulses, respectively. Each operation of relay |1| closes the circuit for operating the pen register electromagnet |03 so as toV mark the pen register tape for each impulse. The electromagnet 1| 02 isoperated at the beginning vof each digit slightly, in advance of the operation of yelectromagnet |03 so as to insure a full length mark for the iirst impulse and to separate the markings for veach train lof dial impulses. Y If the tape is not already in motion when the electromagnet |03 is operated responsive to the rst dial impulse, the impulse mark may be too short for positive identication due to the inertia of the pen register mechanism. Relays |1| and |12 provide a timed closure for pen register electromagnet |03. Being slow to release, relays |13v and |14 remain operated under control of relays |65 and` |1| during response to each train of dial impulses. If the dial impulses are short so that relay |54 reoperates Aas soon as relay |65 operates, relay ,|10 is not locked under control of relay |54;and relay |10 releases as soon as relay |65 releases. In order to hold relay |10 operated long enough to eectthe operation of relay |1|, relay |65 is `rendered slightly slow to release by connecting the non-inductive resistor |61 in parallel with the winding of relay |65.

When relay 34 of the selector SI operates to transfer the line Ll from the windings of relay 35 to the line relay of the next switch of the train, battery through the lower vwinding ofrelay 35 may be disconnected from the ring conductor of line LI before ground through the upper winding of relay 35 is disconnected from the tip conductor of the line; and the control grid of valve |50 will be connected to ground through the upper winding of relay 35 while the negative battery through the lower winding is disconnected. Current in the anode-cathode circuit of valve |50,then effects a voltage drop through resistor |52 which renders the control grid of tube |53 negative with respect to the cathode of tubeV |53, andrelay |54 may start to release; but Valves |40 and |43 operate to prevent an impulse registration. Since at the time relay 34 is operatingthe control grid ofivalve |40 is connected through the station loop and the upper winding of relay 35 toground, th'e grid is rendered positive with respect to itscathode; and the current inY the anode-cathode circuit of valve 40 effects a voltagedrop through resistor` ,|42v which renders the control grid'of Valve |43' positive with respect to its cathode, causing the release of relay |44. f Sincethe capacty of condenser |32 is lessA than that of condenser |,35, valves |40 `and |43 respond .to the operationV ofl relay` 34 slightly in advance of the response of vvalves|5|l and |53. Consequently the release of relay |44 connects negative battery throughrresistor |45, the backcontact of relay |44, and conductor |36 to the control grid of valve |50 to bloclfvalve, |50; Vand before relayv |65 can operate, relay |54 is reoperated by current in the anode-' cathode'circut orvalve |53. Thus the momentaryjrelease vof relay ,|44 prevents the registration ofjan' impulse when the connection is switchedfrom one selector to the next.

The control grid of valve |50 is normally connected to ground through condensers |35 `and |31 in parallel, the'capacitance thus connected between the control grid of valve 50 and ground beingsuch as to enable satisfactoryioperationof valve |50 responsive toV dial impulses transmitted to the line relays of step-,by-step selectors or connectors; but when the call is one completed over a trunk to the central oiice and the dial impulses are being transmitted to the line relay 80 of the connected register sender; and the characteristics of this line relay arev such as to require a smaller capacitance to enable satisfactory operation of valve |50 than is required when the dial impulses are being transmitted to the line relay oi.' a step-by-step selector or connector. The counting relays are provided to count the impulses created by the dialing of the iirst digit; and, if the central ofce code digit 9 is dialed to operate selector SI to select the level giving access to trunks to the central oiiice, counting relays |83 and |86 will also be operated responsive to the dial impulses. When relay |13 releases, at the end of the train, a circuit is closed for operating relay |90 before relay |14 releases; this circuit is traced from the winding of relay 90, inner upper front contact of relay |33, outer lower front contact of relay |86, front contact of relay |14, back contact of relay |73, conductor |23, front contact of relay |22, and front contact of relay |2| to ground. The release of relay |74 opens this circuit but relay |90 locks under control of relay |86 to the same ground. The operation of relay |90 disconnects ground from conductor |80 to release the counting relays which are operated, and disconnects ground from conductor |38 so that condenser |35 alone connects the control grid of valve |50 to ground. Valve |50 will then respond satisfactorily when the succeeding.trains of dial impulses are transmitted to the impulse relay 80 of the register sender in the central oiiice. Relays |86 and |00 remain operated so that the counting relays are not operated re sponsive to the succeeding trains of impulses.

If the lrst digit dialed is any other than the digits 1 or 9, the release of relay |13 at the end of the last impulse of the train closes a circuit for operating relay |9|. When relay |14 releases, the circuit for operating relay ISI is opened; but relay |9I is locked through conductor |23 until the calling subscriber releases the connection. The operation of relay ISI prevents the operation of the counting relays responsive to the succeeding -digits dialed at the subscribers station. If a preliminary impulse is created prior to connection of the line LI to a rst selector, relay |54 releases and reoperates; but relay |55 is not operated because battery is not connected to the winding of relay |65 until relay 8 has operated. If the rst digit dialed is the digit 1, or a preliminary impulse is created after the operation of relay I8, relay |65 will operate and the counting relay 8| will be operated. When relay |13 releases at the end of this impulse, relay |90 is operated thereby causing the release of relays I l5, I'II and` ISI.

The release of relay |8I causes the release of relay |90 since the locking path of relay |90 includes a front contact of relay I 86. The counting relays are now ready to respond to the impulses created by the dialing of a rst digit other than the digit 1.

When the callvinitiated at station A is ended by restoring the telephone to normal, the switches are restored to normal and the disconnection of ground from conductor I4 causes the successive release of relays ||4 and ||8. The release of relay ||8 extinguishes the lamp L at the service observing position, and causes the release of relays |2| and |22. The release of relay |2I closes a, circuit for operating relay |26, disconnects the control grids of valves |40 and relay |24 releases electromagnets |00 and |02;

and the release of relay |26 prepares the time and impulse recorder for the next call. If relay |2I is reoperated by the initiation of a new call before relays |24 and |25 have completed their operations, relay |26 is held operated under control of relay |25 so that the time stamp is operated only once. In this case, relay |26 closes a temporary circuit through its inner lowerfront contact for holding relays 2| and |22 operated until relay |I8 is operated.

If the line LI is seized by a connector CI on an incoming call, the ground connected through' the sleeve brush to conductor I3 to effect the operation of cut-oli relay I6 also causes the successive operation of relays I|4 and IIB. Relay ||8 lights lamp L at the observing operators position and opens the circuit for operating relay |20 before relay |20 can be operated. When such a connection is released, the disconnection of ground from conductor I3 causes the successive release of relays ||4 and |I8 to extinguish the lamp L.

It is of course obvious that thecentral oiice code may be a digit other than "9 and that the central office code may consist of more than one digit.l AIn any case, the arrangement would be such as to effect the change in grid capacity at the end of the centralofce code.

What is claimed is:

1. In a service observing equipmentconnected to a subscribers line and comprising impulse responsive means and means for recording dial impulses transmitted over said line, means for counting the impulses of a train of impulses transmitted over said line, means for preventing the response of said impulse counting means to succeeding trains of impulses, and means rendered effective by said counting means inthe event said train of impulses consists of a particular number of impulses to vary the capability of the impulse responsive means.

2. In an impulse controlled switching system, al line, means for transmitting trains of current impulses over said line, switching means selectively controlled by said trains of impulses, impulse responsive means connected to said line,

means controlled by said impulse responsive means for counting the impulses of a train transmitted over said line to said switching means, means effective only if said train consists of a particular number of impulses to vary the` capability of said impulse responsive means, yand. means for preventing the operation of said counting means responsive to trains of impulses following said train.

3. In a communication system comprising subscribers stations and lines, impulse transmitting means at each station and impulse controlled switching means for establishing connections between lines, means connected to one of said lines for responding to trains of impulses transmitted over said one line to said switching means, means controlled by said impulse responsive means for counting the impulses in a train transmitted over said line, means for preventing the geraete counting of'the impulses of 'trains following said i,r'ain, a'nd` means eiective only if said train consists of a particular number of impulses to change the. capability 'of said impulse'responsive means. L 4'. In a communication system comprising' a subscribers station and line, impulse transmitting means at said station, impulse responsive means of a first character, impulse responsive means of a second character, means including a selector connected to said line and responsive to impulses transmittedv from said station over said', line for extending the connection from said line to said impulse responsive means of said, first character or to said impulse responsive means of said second character, other impulse responsive means connected' to said line, and means controlled by said other impulse responsive means for changing the capability of said other impulse responsive means upon extensionof. the connection from said line to said impulse responsive means of a second character. but notl upon exten-V vsion of" the connection from said line to said impulse responsive means of a iirst character.

5. In a communication system comprising a subscribers'station and line, impulse transmitting means at said station, impulse responsive means of a irst character, impulse responsive means of a second character, means including a selector connected. to said line and responsive to a first train of impulses transmitted Vfrom said station over said line for extending the connection from saidv lin'e to said impulse responsive means of said first character or to said impulse responsive means of said second characterdepending'upon the number of impulses insaid first train, other impulse responsive means connected to said' line, and means including impulse counting means controlled by said, other impulse responsive means for changingtine capability of said other impulse Vresponsive means upon cxtension of, the connection from said line to said impulse responsive means of a secondy character but not upon extension ofthe connection from said line to said impulse responsive means of ai'lrst character.

6. In a communication system comprising a impulse transmitsubscribers station and line,

a first impulse reting means at said station,

-sponsive means, a second impulse responsive means, a third impulse responsive means, a fourth impulse responsive means, said rst and second impulse responsive means being of a first character, said third impulse responsive means being4 ofa second character, means connecting said first impulse responsive means to said line, meansincluding aselector controlled by said first impulse responsive means for extending the connection from said line to said second impulse responsive means or to said third impulse responsive means depending upon the number' of impulses in a train transmitted from saidistation over said line, means connecting said fourth impulse responsive means to said line, and means including impulse counting means controlled by said fourth impulse responsive .means for changing-the capability of said fourth 'impulse responsiveV means upon extension of the connection froml said line tov saidthird impulse responsive means but not upon extension of the connection from-said line to saidv second'impulse responsive means.

'7; In a switching system, a line, a station comprising-impulse transmitting means connected to said line, arst selector, means connecting said'rst selector to said line,` impulse-responsive means ir'r said selectorV controlled over said line bythefmpulse transmittingmeans at said" station, other selectors each having impulse responsive means similar to the impulse responsive means of said iirst selector, said other selectors connected to terminals in one or more levels of the bankof said first selector, a group of trunks connected to the terminalsl in another level of the bank of' said selector, register senders each including impulse responsive means of ai char;- acter differenty from the impulse responsive means of' said iirst' selector, means in said first selector controlled by the impulse responsive means therein for selecting an idle one ofY said other selectors or an idleA one of said' trunks depending upon the number of impulses in a train transmitted over said line from said station to said selector, means responsiveY to theselection of one-of said' trunks forextending the connection of said line over said one trunk` to the, impulse responsive means of an idle one of said register senders, other impulse responsive means connected to said line for response to all ofthe trains of impulses transmitted over said line, means controlledl by said otherimpulse responsive means for changing the capability of said other impulse receiving means in the eventI said impulses eiiect the selection of one of said Atrunks by Vsaid first selector.

8. In a switching system, a line,` a station comprising impulse transmitting means connected to said line', a iirst selector, means connecting said first selector to said line, impulse responsive means in said selector controlled over said line by the impulsev transmitting means at saidstation, other selectors eachA having impulse responsive means similar to thev impulse responsive means of saidiirst selector, said other selectors connected to terminals in one or more levels of the bank' of saidiirst selector, a, group of trunks connected to the terminals inl another level of the bank of 'said selector, register senders each including impulse responsive: means of a character diierent from the impulse responsive means of said first selector, means in said first selector controlled by the impulse responsive means therein for selecting anidle one of said other selectors Aor an idle one of said trunks depending upon the number of impulses in a train transmitted over said line from said station' to said selectors, means responsive Ito the selection of one of said trunks for extending the connection of said line over said onel trunk to the impulse responsive means of an idle one of said register senders', other impulse responsive means connected to said line for` response tol all ofthe trains of impulses transmittedV over said line, means controlled by sai-d other impulse responsive means for counting the'impulses which effect the operation of said first selector to select one o'fsaid other selectors or to select one of said trunks, means controlled by said counting means for changing the capability of `said other impulse receiving means inthe event said impulseseffect the selection of one of said trunks by saidjiirst selector, and means for preventing the counting of trains of impulses transmitted over said line following the train which selectively'controls the operation of said iirstselector.

9. In combination in a 'signaling-system, a, line over which train ofV current impulsesA are transmitted, a thermionic valve, means connecting the control grid of said valve to a conductor of said line, means including a battery havingV its positive pole connected to' groimdv for rendering pulse relay, means for effecting the operation of said relay when said control grid is negative and for eiecting the release' of said relay when said control grid is positive With respect to said cathode, counting means controlled by said relay, and means operated in the event a train of impulses transmitted over said line consists of a particular number of impulses for changing the capacitance of the connection between the control grid and ground.

10. In a combination according to claim 7, means eiective to prevent the operation of said counting means in response to trains of impulses following a rst train transmitted over said line.

11. In combination in a switching system, a line, a group selector, means connecting said selector to said line, a station comprising an impulse transmitter, second selectors connected to a group of terminals in the bank of said first selector, impulse receiving means in said iirst selector responsive to a rst train of impulses transmitted over said line, means in said rst selector for selecting an idle set of terminals in the group identified by said rst train of impulses, impulse receiving means in the second selector connected to a selected set of terminals in the bank of said rst selector, means in said rst selector effective to transfer said line from connection with the impulse receiving means of said rst selector to the impulse receiving means of the selected second selector, a rst thermionic valve, means connecting the control grid of said valve to a first conductor of said line, means including a battery having its positive pole connected to ground for rendering said control grid negative with respect to the cathode of said valve when no impulse is being transmitted over said line and for rendering said control grid positive with respect to said cathode when an impulse is being transmitted over said line, an impulse relay, mea-ns for eiecting the operation of said relay when said control grid is negative and for effecting the release of said relay when said control grld is positive with respect to the cathode, means controlled by said impulse relay for recording the impulses transmitted over said line, a second thernnonic valve, means connecting the control grid of said second valve to a second conductor of said line, means including said battery rendering the control grid of said second valve negative with respect to its cathode while said line is connected to the impulse receiving means of said rst selector and to the impulse receiving means of a selected one of said second selectors and for rendering the control grid of said second valve positive with respect to its cathode in the event said transfer means in the first selector ydisconnects said iirst cond-uctor of the line from the impulse receiving means of said lirst selector before it disconnects said second conductor of the line from the impulse receiving means of said first selector, and means rendered effective when the control grid of said second valve becomes positive with respect to its cathode for rendering the control grid of said rst valve negative with respect to its cathode so as to prevent release of said impulse relay for a long enough interval of time to effect the operation of said recording means when said transfer means in said first selector is operated, thereby to prevent a false operation of said recording means.

FREDERICK R. LAMBERTY.

REFERENCES CITED The following references are of record in the iile of this patent:

UNITED STATES PATENTS Number Name Date 2,318,333 Logan et al. May 18, 1943 1,943,130 MacPherson Jan. 9, 1934 1,848,174 Irvine et al. Mar. 8, 1932 1,194,378 Goodrum Aug. 15, 1916 

